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This article in Time magazine suggests that engaging in challenging mental tasks may be associated with lower rates of mental decline in older adults.
The article states that:

In one study, presented last year at the Cognitive Neuroscientist
Society's annual meeting, psychologist and neuroscientist Helena
Westerberg of the Karolinska Institute in Stockholm compared the
cognitive abilities of 45 young adults (average age 25) with those of
55 older adults (average age 65). She found that after five weeks of
computerized training on tasks ranging from reproducing a series of
light flashes to repeating digits in the opposite order that they were
given, the older group was able to reach the same level of working
memory, attention and reaction time that the younger group had at the
outset. (Notably, the younger group had even greater improvements by
the end of the training period.) "The program is always pushing them
to do better," says Westerberg, who notes that an advantage of
video-game training is that the programs' difficulty level continually
adjusts upward to match players' evolving abilities. "They have
feedback and can see their scores."

This might suggest that scientists and professors might have less decline in fluid IQ with age. Is there any support for this idea?

Active mental practice is not necessarily more associated with professors and scientists than others. Does a musician do only physical practice? We can restate by relating the title and the body of the question.
–
KrisJan 19 '12 at 10:30

1 Answer
1

Seattle Longitudinal Study:

You might want to have a read about The Seattle Longitudinal Study of Adult Intelligence.
There's a summary of the study on this website.
To quote the website:

The Seattle Longitudinal Study of Adult Intelligence has followed a
group of more than 5000 people for well over four decades. The program
began in 1956 and participants have been tested across a whole gamut
of mental and physical abilities at seven year intervals since that
date.

With regards to preventing cognitive decline the website suggests that

The following variables may reduce the risk of cognitive decline in old age:

absence of chronic diseases

a complex and intellectually stimulating environment

a flexible personality style at mid-life

high intellectual status of spouse

maintenance of high levels of perceptual processing speed

If these general points are true, then presumably an argument could be made that scientists and professors have more complex and intellectually stimulating environments. However, the age related declines may be most pronounced in what are potentially post retirement ages (e.g., 60 or 70 +), where the environment would be different.

Some general points

Professors and scientists have some of the highest levels of intelligence among the professions (see this table based on this working paper by Hauser, 2002, PDF). Thus, if everyone did decline cognitively at an identical rate, people from such professions would still tend to have higher intelligence (e.g., a 10-point decline from 130 is 120, versus 90 to 80). So, people with initially high intelligence even with decline can still be intelligent. However, this initially high intelligence is most likely due to genetics or some undefined source than to the stimulation of the profession itself.

Thus, indirectly, the above points (high intelligence of scientists and professors) and potentially environmentally stimulating environments suggest that they will be more intelligent at older age. But my guess is that most of that effect will be due to base line differences in intelligence.

Very interesting answer. I noticed that lot of IQ tests (RPM or California) have different norms for age groups. So how they measure decline of IQ. Is it decline of IQ as apsolute mental strength? Or drop in numbers measured by specific test?
–
ICanFeelItJul 27 '13 at 17:03